Simplify the following expression: $n = \dfrac{z}{5} - \dfrac{9z}{2}$
Answer: In order to subtract expressions, they must have a common denominator. The smallest common denominator is the least common multiple of $5$ and $2$ $\lcm(5, 2) = 10$ $ n = \dfrac{2}{2} \cdot \dfrac{z}{5} - \dfrac{5}{5} \cdot \dfrac{9z}{2} $ $n = \dfrac{2z}{10} - \dfrac{45z}{10}$ $n = \dfrac{2z -45z}{10}$ $n = \dfrac{-43z}{10}$